1. Field of the Invention
This invention relates, generally, to dentistry. More particularly, it relates to a model and die system for making casts of dental impressions for the shaping of crowns and dentures.
2. Description of the Prior Art
The use of triple trays is now the most common technique for taking impressions. Also known as dual-arch trays, they capture the area to be restored, the opposing area, and the bite relationship. Errors can arise, however, when a bite registration is transferred from a triple tray impression to an articulation hinge such as a VertexÂ®, OrbizÂ®, QuickulatorÂ®), or to a generic metal articulation hinge.
The current method for transferring a bite registration from a triple tray to an articulation hinge includes the initial step of mixing dental stone powder to make a batch of liquid dental stone and pouring the liquid dental stone into the impression on the prep side first. The stone is allowed to cure for about thirty (30) minutes. Another batch of liquid stone is then poured into the opposing side of the impression and allowed to cure for about thirty (30) minutes at which time the model of the teeth is removed.
The model with the prepared teeth is then ground on a model trimmer. The bottom of the model must be completely flat all the way across. A router or a hand piece and burr are then used to bevel the model edges. The model is then dried and cleaned.
Holes are then drilled in the bottom of the model in registration with the preps and other sections of the working model. The model is then cleaned again.
Next, dowel pins are glued into the holes. Typically, there are two dowel pins for each section. The glue is allowed to set and dry. A separating agent is then sprayed onto the bottom of the model. After the separating agent has dried at least slightly, a batch of working quadrant stone is then prepared and poured into a working quadrant former. Model pins are then inserted into the working quadrant former. The working quadrant stone is allowed to set in accordance with the manufacturer's suggested time, which is usually around thirty (30) minutes. The model teeth are then removed from the working quadrant with the pins exposed. The bottom of the working quadrant is ground to expose the die pinholes. The holes are then cleaned of debris and the model is cut into sections using a hand piece and disc or a die saw. The dowel pins are then cleaned because the separating medium leaves a film on the dowel pins that can hinder the die section and other sections of the model from seating down all the way in the working quadrant. The crown or denture being prepared will not fit the patient if the sections and dies do not seat all the way flat into the working quadrant stone.
The opposing arch is then removed from the impression. It is trimmed on a model trimmer and placed in a working quadrant former. A batch of stone is mixed and poured into the working quadrant former to hold the opposing arch. After the stone has set for about thirty (30) minutes, the technician then articulates both arches.
Articulation is currently performed by hand and eye to try and “guess” where the correct centric bite is located. A hinge is then glued into place to maintain the bite that has been deemed to be the correct bite. This completes the working model and the case is ready to proceed with fabrication of the restoration.
This method is very labor-intensive and mistakes at any step can result in a substandard working model. For example, it is difficult to always achieve the optimal water and powder ratio to produce the working quadrant stone. Further steps that are difficult to optimize include the grinding of the model, the placement and gluing of the dowel pins, and the articulation of the models to produce proper occlusion in the mouth. Further difficulties include breaking the model during drilling or trimming of holes which necessitates re-starting the process from the beginning, and the optimization of many other variables not expressly mentioned herein but well-known to those who work in this field.
Several techniques have been developed in an effort to improve the above-described process. Some technicians, for example, have developed their own articulation hinges in an attempt to avoid use of the above-mentioned commercially available articulation hinges. Moreover, the model has been placed in the center of the tray but this technique has the disadvantage of making the prep hard to reach and hard to see.
Most of the known systems prevent the technician from determining whether or not the dies are completely seated. Moreover, in all of the known systems it is difficult to put in and take out the dies from the working quadrant. Most known systems do not provide good centric opposing quadrants for occlusion nor do they provide a free and centric opposing quadrant. Nor does any known system employ double dowel pins to stabilize dies.
What is needed, then, is a system that is much less labor intensive than the known systems. The needed system would reduce the amount of guesswork, artistry, and skill required under the known systems. It would therefore standardize the procedure and enable a technician to work with ease and accuracy. The resulting models would be superior to the models made under the current system.
More particularly, an optimal system would enable a technician to use any of the commercially-available articulation hinges. In an optimal system, the dies would always be placed in a labial position so that they would be easy to reach and see. An optimal system would provide a flat working quadrant with no obstructions so that it can be determined whether or not the dies are properly seated. Each die and model section should be double dowel-pinned and each die should have an exact, easy path of insertion. Movement should always be solid, never centric. The improved system should also provide a complete mesial or distal centric opposing quadrant.
U.S. Pat. No. 4,382,787 to Huffman discloses a dental model articulator for mounting and holding dental model casts necessary for the correction or alteration of teeth. The articulator includes two mirror-image brackets, connected together through a hinging mechanism, that are attached to a mounting means. Huffman further discloses a mechanism including a working quadrant with an opposing element for securing dental molds. This ensures that the bite between the lower and upper casts is optimal. Huffman does not include pin-receiving bores in a working quadrant nor does Huffman disclose elevated mounting members located in an opposing quadrant.
U.S. Pat. No. 6,471,513, also to Huffman, discloses a dental model working quadrant assembly having preformed apertures for securing or reconstructing a dental model. The supporting working quadrant includes apertures situated in two rows located between indexing studs. Two rows of apertures are contained in the support structure, with the external aperture row being offset from and adjacent to the internal aperture row. These apertures are designed to receive tapered pins. The working quadrant may be attached to an articulator either through an articulator plate or through the use of a latch and a slot located on the mounting working quadrant.
A mechanism with lower and upper support means that produces a more accurate recreation of restorative work is disclosed in U.S. Pat. No. 5,466,152 to Walter. The support means is connected at one end through the use of an anti-rotational guide located at a hinged end. A plurality of indexing holes are situated throughout the surface of the support member. The dental model is affixed to the support member through the attachment of indexing pins corresponding to predetermined indexing holes. A hinge and indexing pins stabilize the support working quadrant and opposing structure and thus produce a fairly accurate representation of a dental restoration model. There are no offset, preformed bores that enables the efficient trimming of excess casting material.
In view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the current systems could be improved.